Creating a version 2 that assumes C++11 is likely the best route for end user experience, as it would create a clear boundary as to what they can use. However, it would need to be done so that library maintainers do not have to work on two versions unless they choose to do so. Perhaps once the move to Git is done a Boost 2 super project could be created, and libraries that require C++11 would only appear as sub modules for it. Then libraries that are not C++03 compatible (or depends on another that is not) would be easy to find during testing since they will not compile. -----Original Message----- However, IMHO, boost should move to a 2.0 version to advocate plain C++-11 without looking back to legacy compilers. As soon as the compiler landscape evolves to support more an more C++11 features, everyone is able to benefit from such a solution. The Boost 1.X line however should remain C++03 compliant.